The present invention refers to a piston stroke limiting device for a reciprocating compressor of the type driven by a linear motor and applied to refrigeration systems used in small refrigerating appliances, such as refrigerators, freezers, drinking fountains, etc.
In reciprocating compressors with a linear motor, the gas compression mechanism occurs by the axial movement of approximation and separation of a piston inside a cylinder, in relation to a cylinder head which is mounted to a cylinder end and where suction and discharge valves are provided for regulating the admission and discharge of the gas in relation to the cylinder.
The piston is driven by an actuator, which sustains a magnetic component actuated by the linear motor. The piston is connected to a resonant spring, with which it forms, together with the magnetic component, the resonant assembly of the compressor.
This resonant assembly has the function of developing a linear reciprocating movement, making the movement of the piston inside the cylinder exert a compression action on the gas admitted by the suction valve, up to the point in which said gas may be discharged, through the discharge, to the high pressure side of the refrigeration system to which the compressor is mounted.
Variations in the operational conditions of the compressor, or variations in the feeding pressure may make the resonant assembly displace beyond an acceptable limit, making the piston top strike the cylinder head, causing damages to the compressor. Several forms for controlling the travel of the piston have already been proposed, both the electronic forms (U.S. Pat. Nos. 5,156,005, 5,342,176, 5,450,521, 5,592,073), which control the current supplied to the motor, as a function of the piston position, and the mechanical forms (usually employed in Stirling machines), such as the provision of gas discharge channels, or pneumatic or mechanical springs. Electronic controls, which are able to precisely control the piston position, are extremely expensive, besides presenting an inherent inertia to the system. The same occurs with the mechanical solutions. Such inertia allows the occurrence of occasional impacts, which, with time, cause damages to the top of the piston and the cylinder head.
Thus, it is a general objective of the present invention to provide a reciprocating compressor with a linear motor, of low cost and easy construction, which minimizes the occurrence of impacts of the piston against the cylinder head, without presenting the constructive inconveniences of the known prior art solutions.
These and other objectives are attained by a reciprocating compressor with a linear motor, comprising a piston reciprocating inside a cylinder having an end closed by a cylinder head provided with suction and discharge orifices, to which are operatively associated suction and discharge valves, said compressor comprising a valve means mounted inside the cylinder and having an operative position, seated against the discharge orifice, and an inoperative position, spaced from said discharge orifice, the operative position being defined when the top of the piston is within a certain distance from the cylinder head, said distance being defined, so that, at the end of the compression stroke of the piston, be reached inside the cylinder a determined pressure that will result in a force on the piston opposite to that force which is impelling said piston and which is sufficient to interrupt its compression stroke before impacting the cylinder head.